Communication systems typically include logic and hardware to transmit data from an origin to a destination. In particular, communication systems have routing or switching logic to make high-level decisions that select ports, routes, and media for transmitting the data. Communication systems also include links, each having a transmitter, a medium, and a receiver, to transmit the data in response to those high-level decisions.
The origin clocks the data originally. Then, each intermediate link, or more specifically, the link's transmitter typically clocks the data and transmits to the link's receiver or the destination.
Devices such as routers typically access a network identification (NETID) for the data transmission to determine the destination and calculate the route to the destination through intermediate links based upon a routing protocol and a routing table that includes information about the communication system's topology. The routing protocol dynamically determines routing for the data transmission, taking into consideration changing conditions of the communication network such as unavailable links. Routing tables, for instance, may associate links with ports, or port numbers, through which the data transmission should be routed.
Upon determining the port for the data transmission, the transmission is routed through that port to the destination or another, intermediate destination. Some of the more complex routers, such as routers for super computers, may also select a medium through which the transmitter and receiver will transmit the data.
The transmitters and receivers may consume more power depending upon the data transmission and the media through which the data transmission is routed. In particular, data transmissions at higher data frequencies, with difficult data traffic types or patterns, via long media, and/or via lossy media, require amplifiers and complex, mixed-signal circuitry. The amplifiers and complex, mixed-signal circuitry improve or maximize the sampling window for bits of data in the data transmission to maintain an acceptable bit error rate (BER), i.e., the number of misinterpreted bit values for the data transmission.
Higher data frequencies require internal circuits of transmitters and receivers to operate at high clock frequencies and, thus, high voltage levels, to sample and re-transmit the data in each intermediate link. Further, when the clock frequencies of a transmitter and receiver pair have differences in phase that change over time, often referred to as spread spectrum signaling, the receiver may include a clock and data recovery (CDR) loop with second and, possibly, third order frequency tracking circuits running at high internal frequencies.
Similarly, demanding traffic types, which include patterns that do not often switch between logical ones and zeros or that switch between ones and zeros in irregular or sporadic patterns, require complex internal circuits of transmitters and receivers that may operate at high clock frequencies to capture the relatively few transitions. The phase of the sampling clock is adjusted based upon the phase of the data signal as determined from those relatively few transitions.
With regards to long and/or lossy media, the amplitude of the data transmission may attenuate in a frequency-dependent manner. Amplification and pre-emphasis by the transmitter as well as amplification and equalization by the receiver accentuate certain frequencies to increase the sampling window. Other circuitry such as internal loop filters may be more complex when the media is long and/or lossy.
The amplification and complex, mixed-signal circuitry, however, significantly increase the overall power consumption for the communication system. For example, serial links within a large interconnect system such as a super computer may consume 20 to 37% of total power consumption.
Further, the amplifiers and complex, mixed-signal circuitry continue to operate at full power even when such circuitry is unnecessary. For example, a high-level decision may make a link inactive or switch the media for the link from a long medium that requires the complex, mixed-signal circuitry, to a shorter medium that does not require such circuitry.
Thus, there is a need for methods and arrangements for power reduction in link circuits such as transmitters and receivers based upon global, or high-level, decisions such as the activity, data transmission frequency, communications media, and traffic type associated with links.